Before throwing money at your problem, check the basics.
1) Verify that the vacuum canister holds a vacuum meaning the diaphragm is not torn. Do a quick search on youtube for videos checking these.
2) Remove your distributor cap, and apply vacuum pressure to your vacuum advance canister. Watch your points plate. This should cause it to move. This movement advances the timing when the engine is idling and cruising without load. (The idling timing will be impacted only if connected to manifold vacuum)
3) Verify your base timing really is 10 degrees btdc like you believe. Remember this is measured without the vacuum advance connected. If you check your timing with the vacuum advance connected, it should register greater than the base timing.
I suspect that at least number 3 above is not right. Perhaps items 1 and 2 need attention as well. After all, these checks are easy to do and may shine light on your issue.
Last edited by Rufus68; 04-21-2017 at 04:18 PM.